Mica
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The mica group of minerals are aluminosilicates with various metals. They split into fine sheets.
Mica includes several closely related materials having perfect basal cleavage.
All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.